Daysleeper: Using class instance variable

March 04, 2007

Using class instance variable

We all know how evil class variables are, and they are as dangerous as the “three headed dog” at the dungeon and we shall not talk about it.

But they are necessary for many of the thingies ruby does and used extensively.But today we shall not talk about them.

We saw earlier that, although class instance variables are excellent, but not so friendly to use and they make Ruby look like C++(ahem).

Here goes a little hack, that allows you to define class level attributes based on class instance variables. Since, i often use it in rails and they have taken cattr for class level attributes.

class Object
  def self.metaclass; class << self; self; end; end
  def self.iattr_accessor *args
    metaclass.instance_eval do
      attr_accessor *args
    end
    args.each do |attr|
      class_eval do
        define_method(attr) do
          self.class.send(attr)
        end
      end
    end
  end
end

What above code does is, creates those class instance variables at class scope and also creates accessor methods for it, so that it doesn’t have to suck when used from class instances(remember @foo.class.i_am_class_instance_var)

Here is a sample that, shows it in action:

class Foobar
  iattr_accessor :foo
end
Foobar.foo = "Hemant"
p Foobar.foo
lol = Foobar.new
p lol.foo

Did i miss anything? comments?

Posted at 10:27 PM in ruby | Permalink

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Comments

Useful code, but I think naming the generator-method iattr_accessor is a bit misleading. What is 'i' supposed to stand for ? I'd advocate naming the method class_attr_accessor because we are talking about 'attributes of the class object'. Other names could be possible, but just adding 'i' to the normal attr_accessor isn't visually compelling enough. Mistakes would be likely.

Posted by: kesV | March 09, 2007 at 10:01 AM